The invention relates to a fundus camera, in particular, to such a camera which facilitates a relative positioning of the camera with respect to an eye being examined.
A conventional fundus camera includes two essential parts, a main body having an optical system and a rack which supports the main body. By changing the relative position between the main body and the rack, the visual axis of an eye being examined is brought into alignment with the principal optical axis of an objective. Referring to FIG. 1 for a description of a conventinal fundus camera, it includes a base 1 which is placed on a desk, for example. A carriage 2 is disposed on the base 1 so as to be movable in a horizontal plane in a fore-and-aft direction and also in a lateral direction. The carriage 2 is provided with an operating handle 3 which permits a movement of the carriage 2 in the horizontal plane. A main body 4 internally houses an optical system which includes an objective 4a located on the front end or on the left-hand end, as viewed in FIG. 1, and an eyepiece assembly 4b located on the rear end or on the right-hand side. A support shaft 5 depends downwardly from the bottom of the main body 4 and is fitted into a holding sleeve 6 which is fixedly mounted on the carriage 2, thus supporting the main body 4. An operating ring 7 is disposed around the upper end of the holding sleeve 6 in concentric relationship therewith for angular movement thereabout to change the degree of fitting engagement between the shaft 5 and the sleeve 6 through means such as a helicoid screw, not shown, thereby changing the vertical height of the main body 4 relative to the carriage 2. A support member 8 extends forwardly and upwardly from the front end of the base 1 and fixedly carries a chin receiver 9 on its top end.
FIG. 2 shows an optical system which may be disposed within the main body 4. Specifically, it includes an objective lens 12 located in opposing relationship with an eye 11 to be examined, an apertured reflecting mirror 13 located rearwardly of the objective lens 12 at an angle of 45.degree. with respect to the principal optical axis of the lens 12, a relay lens 14 disposed further rearward of the apertured reflecting mirror 13, a light path switching mirror 16 rockably disposed between the relay lens 14 and a photographic film 15, a mirror 17 disposed above the switching mirror 16 to form an observation light path, and an eyepiece 18 disposed in opposing relationship with the mirror 17.
In the conventional fundus camera thus constructed, the visual axis of the eye 11 of the patient being examined who has his chin placed on the chin receiver 9, is brought into alignment with the principal optical axis of the objective lens 12 by suitably operating the handle 3 and the operating ring 7 to move the main body 4 in fore-and-aft and lateral directions as well as in the vertical direction while observing, from the lateral direction, the location and the degree of defocusing of an image of an annular slit (not shown), which is disposed in an illumination system, on the front portion of the eye 11. When the visual axis of the eye 11 is brought into alignment with the principal optical axis of the objective lens 12, illuminating light from a light source which has passed through the annular slit impinges from below in a direction indicated by arrow a, and is reflected by the apertured reflecting mirror 13 to pass through the objective lens 12 to illuminate the fundus oculi of the eye 11 being examined. Reflected light from the fundus oculi passes through the objective lens 12 and a central aperture 13a formed in the reflecting mirror 13 and is then successively reflected by the mirror 16 and the mirror 17 to reach the eye 19 of a viewer through the eyepiece 18. In this manner, the viewer is capable of observing an image of the fundus oculi of the eye 11. Under the condition that a good image of the fundus oculi is observed, the switching mirror 16 may be turned in a direction indicated by arrow b until the phantom line position is reached where it is located out of the principal optical axis, whereupon the image of the fundus oculi of the eye 11 is focused onto the photosensitive surface of the film 15, permitting a picture thereof to be taken.
However, it will be appreciated from the foregoing description that with the conventional fundus camera, the entire main body 4 must be moved in order to bring the visual axis of the eye 11 into alignment with the principal optical axis of the objective lens 12, thus disadvantageously requiring a large and complex moving mechanism.
In addition, each time the main body 4 is moved, the location of the viewer's eye must be changed, causing inconvenience in the operation of the arrangement.